1. Field of the Invention
The present invention relates generally to audio sounds and, more specifically, to a method and apparatus for customizing HRTFs (Head Related Transfer Functions) of listeners to provide more convincing and pleasurable 3D (three dimensional) audio works.
2. Description of Related Art
Some newly emerging consumer audio devices provide the option for 3D sound, allowing a more realistic experience when listening to sound. In some applications, 3D sound allows a listener to perceive motion of an object from the sound played back on a 3D audio system.
Extensive research has established that human localize sound source location by using three major acoustic cues, the interaural time difference (ITD), interaural intensity difference (IID), and head-related transfer functions (HRTFs). These cues, in turn, are used in generating 3D sound in 3D audio systems. Among these three cues, ITD and IID occur when sound, from a source in space, arrive at both ears of a listener. When the source is at an arbitrary location in space, the sound wave arrives at both ears with different time delays due the unequal path length of wave propagation. This creates the ITD. Also, due to the head shadowing effects, the intensity of the sound waves arriving at both ears can be unequal. This creates the IID.
In order to synthesize a positioned 3D audio source, a particular set of ITD, IID and a pair of HRTFs for two ears are directly measured to construct an HRTF database for listeners. In order to simulate the motion of the sound source, in addition to the varying ITD and IID, many HRTF pairs have to be used to obtain a continuous moving sound image. In the prior arts, hundreds or thousands of measured HRTFs are used to fulfill this purpose. This increases storage space of an apparatus for accommodating the HRTF database. Furthermore, when the HRTF database receives an input signal, it needs to execute complicated comparisons and calculations to make sure a listener heard a 3D audio work, which increases execution time of the apparatus. There is thus a need for a more accurate HRTF model which provides a suitable HRTF for source locations in a continuous auditory space, without annoying mass calculation and storage space.